Tuesday, September 3, 2013

Excavating Dark Deposits

An approximately 250 meter crater has excavated low reflectance material from beneath the lunar surface, west of Sommering P crater, southeast of Copernicus. LROC Narrow Angle Camera (NAC) frame M185955372R; LRO orbit 12483, March 9, 2012; 9.56° angle of incidence, native resolution 1.11 meters per pixel, from 110.79 km over 1.53°N, 249.3°E, field of view 1.8 kilometers [NASA/GSFC/Arizona State University].
Sarah Braden
LROC News System

Amazing ejecta patterns from small, young craters are always something to look at on the lunar surface. Today's Featured Image displays compositional diversity in fresh ejecta. The broad, low-reflectance streaks of material are likely excavated pyroclastic materials. This approximately 250 m diameter crater is located at 2.162°N, 349.401°E, west of the crater Sommering P.

This low-reflectance material is part of a larger area called a Dark Mantle Deposit (DMD). Dark mantle deposits have lower reflectance compared to surrounding mare basalt areas and are also spectrally distinct from mare basalt. In this case, the dark mantle deposit was likely covered by a thin layer of crater ejecta.

Context with Sommering P
The small crater's location marked with a white circle in an LROC Wide Angle Camera (WAC) context image of a field of view 80 km across [NASA/GSFC/Arizona State University].
The opening image has a low incidence angle of 10° which means the Sun is high in the sky (near local noon). High-sun images are good for revealing differences in the reflectance properties of the surface. Low-sun (large incidence angle) images are better at emphasizing morphology due to topographic shading and shadowing. Incidence angle is the angle between the vector of sunlight and the vector normal to the surface. The WAC context image above has a large incidence angle (taken in early morning) which makes visible the topographic high where the crater was formed. This topographic high is a remnant of highland terrain (kipuka) surrounded by younger mare basalt deposits (smooth, flat areas). There are many other craters on the topographic high that excavate low-reflectance material, which suggests that the whole area is different from the surrounding mare basalt deposits. The high-sun WAC mosaic (below) of the same area shows the locations where the dark mantle deposit is visible. You can learn more about dark mantle deposits here!

643nm high sun, high-reflectance WAC context
LROC WAC monochrome (643 nm) high sun, high reflectance view of the same area as seen in the WAC mosaic immediately above, resolution roughly 100 meters per pixel. Note darker material around the area of the topographic high place [NASA/GSFC/Arizona State University].
Explore the full NAC image HERE to see the other craters excavating low-reflectance material.

Related Images:
Hyginus Crater and Pyroclastics
Dark Wisps in Copernicus
Polka-Dot Ejecta
Pyroclastic Excavation

No comments: